Aluminum alloy, bar-like material, forge-formed article, machine-formed article, wear-resistant aluminum alloy with excellent anodized coat using the same and production methods thereof

ABSTRACT

An aluminum alloy containing 5 to 12% (mass %; similarly applicable hereinafter) of Si, 0.1 to 1% of Fe, less than 1% of Cu and 0.3 to 1.5% of Mg and having the valance formed of Al and impurities is cast by a continuous casting process. When the cast mass consequently obtained is homogenized, then extruded and/or forged and/or machined and subjected to an anodizing treatment, the resultant formed article is endowed with excellent wear resistance because the anodized coat formed thereon in a thickness of 30 μm or more with hardness Hv of 400 or more allows the presence therein of eutectic Si particles having particle diameters in the range of 0.4 to 5.5 μm.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is an application filed under 35 U.S.C. §111(a)claiming the benefit pursuant to 35 U.S.C. §119(E)(1) of the filing dateof Provisional Application No. 60/535,501 filed Jan. 12, 2004 pursuantto 35 U.S.C. § 111(b).

TECHNICAL FIELD

This invention relates to aluminum alloys, bar materials, forged partsand machined parts which are capable of providing sleeve parts for usein automobiles, require the hardness and thickness of an anodized coat,shun sustaining a crack and demand wear resistance; wear-resistantaluminum alloys using the aluminum alloys mentioned above and excellingin anodized coat hardness; sleeve parts; and methods for the productionthereof.

BACKGROUND ART

Among other automobile parts, the casts of the ADC12, AC4C, A390 andAl—Si types and the alloys for the Al—Si type expanded materials ofA4032 alloy have been hitherto formed by subjecting extruded materialsand forged materials to the T6 treatment, the machining treatment andthe anodizing treatment, and the parts consequently obtained have beenput to use.

The casts of the Al—Si type and the alloys for the Al—Si type expandedmaterials have their Cu and Mg contents adjusted with the object ofexalting the wear resistance and strength thereof.

Though the alloy materials mentioned above contain Cu in large amountswith a view to exalting their wear resistance and strength, they aresupposed to encounter difficulty in acquiring the thickness and thehardness of an anodized coat.

The concept of limiting the Ni content as an impurity to less than 0.05%has been proposed (Patent Document 1 (JP-A HEI 10-204566), for example).

The material of Patent Document 1 is characterized by containing 6 to12% (weight %, that is applied hereinafter) of Si, 0.1 to 1.0% of Fe,1.0 to 5.0% of Cu, 0.1 ro 1.0% of Mn, 0.4 to 2.0% of Mg, 0.01 to 0.3% ofTi and 0.005 to 0.2% of Sr, limiting the content of Ni as an impurity toless than 0.05% and having the balance formed of Al and impurities,having dispersed in the matrix thereof eutectic Si particles of anaverage particle diameter of 1.5 to 5.0 μm and allowing the presencetherein of 5000 or more and less than 10000 eutectic Si particles ofthis average particle diameter per mm².

However, the material disclosed in Patent Document 1, on being anodized,has formed a film having an unduly low hardness, specifically hardnessHv only in the approximate range of 310 to 370.

The conventional Al—Si type alloys, therefore, have been mostly suchparts as are put to use without undergoing an anodizing treatment. Theparts, that need an anodized coat and have an ability to form the coat,have been applied to products (portions) that have no need for thehardness of the coat. Thus, they have proved useful in markedly limitedapplications and have incurred difficulty in satisfying the demand ofthe market.

In the case of the 6000 type alloys and the 5000 type alloys that have aproper ability to succumb to an anodizing treatment, when the coat isapplied in a thickness 30 μm or more, the coat sustains a crack and thecoated alloy product becomes no longer suitable for the intended use.

This invention, therefore, aims to provide aluminum alloys, barmaterials, forged parts and machined parts which are capable ofproviding sleeve parts for use in automobiles, require the hardness andthickness of an anodized coat, shun generation of a crack and demandwear resistance; wear-resistant aluminum alloys using the aluminumalloys mentioned above and excelling in anodized coat hardness; sleeveparts; and methods for the production thereof.

With a view to accomplishing the object mentioned above, the presentinventors have made a diligent study regarding the characteristicproperties of the Al—Si type aluminum alloys and the anodized coatsformed on the surfaces thereof. They have perfected this invention basedon the knowledge acquired consequently.

DISCLOSURE OF THE INVENTION

The aluminum alloy according to this invention forms in consequence ofan anodizing treatment an anodized coat having a thickness of 30 μm ormore and hardness Hv of 400 or more and allows the presence, in thecoat, of eutectic Si particles having particle diameters in the range of0.4 to 5.5 μm.

Further, the aluminum alloy according to this invention forms inconsequence of an anodizing treatment an anodized coat having athickness of 40 μm or more and hardness Hv of 400 or more and allows thepresence, in the coat, of eutectic Si particles having particlediameters in the range of 0.8 to 5.5 μm.

The aluminum alloy mentioned above contains 5 to 12% (mass %; similarlyapplicable hereinafter) of Si, 0.1 to 1% of Fe, less than 1% of Cu and0.3 to 1.5% of Mg, and has the balance formed of Al and impurities, hasdispersed in the matrix thereof eutectic Si particles having particlediameters in the range of 0.4 to 5.5 μm, inclusive of 60% or more of theeutectic Si particles having particle diameters of 0.8 to 2.4 μm, andallows the presence therein of 4000 or more and less than 40000 eutecticSi particles per mm².

The aluminum alloy mentioned above, when containing 9 to 12% of Si, has80% or more of the eutectic Si particles with particle diameters of 0.8to 2.4 μm.

The aluminum alloy mentioned above consists in substantially no Cu.

The aluminum alloy mentioned above consists in containing at least onecomponent selected from among 0.1 to 1% of Mn, 0.04 to 0.3% of Cr, 0.04to 0.3% of Zr, and 0.01 to 0.1% of V.

The aluminum alloy mentioned above consists in containing at least onecomponent selected from among 0.01 to 0.3% of Ti, 0.0001 to 0.05% of Band 0.001 to 0.1% of Sr.

The aluminum alloy mentioned above consists in being a bar material castby a continuous casting technique.

The aluminum alloy mentioned above in 9) the ninth aspect of the presentinvention consists in being a bar material obtained by subjecting a barmaterial cast by the continuous casting technique further to anextruding process or an extruding and drawing process.

The bar material according to this invention consists in being formed ofan aluminum alloy.

The bar material of this invention consists in being used as a sleevepart.

The bar material of this invention consists in being a forged partformed by subjecting a bar material to a forging process.

The bar material of this invention consists in being a machined partformed by subjecting a bar material or a forced part to a machiningprocess.

This invention further consists in being a wear-resistant aluminum alloyallowing the presence, in an anodized coat, of eutectic Si particles ofparticle diameters in the range of 0.4 to 5.5 μm, forming the coat in athickness of 30 μm or more and with hardness Hv of 400 or more andconsequently excelling in hardness of the anodized coat.

This invention also consists in being a wear-resistant aluminum alloyallowing the presence, in an anodized coat, of eutectic Si particles ofparticle diameters in the range of 0.8 to 5.5 μm, forming the coat in athickness of 40 μm or more and with hardness Hv of 400 or more andconsequently excelling in hardness of the anodized coat.

This invention consists in being a sleeve part resulting from subjectinga machined part to a treatment for forming an anodized coat andconsequently excelling in hardness of the anodized coat.

Further, this invention consists in a method for the production of awear-resistant aluminum alloy excellent in hardness of an anodized coat,comprising casting the aluminum alloy of the composition mentioned aboveto a continuous casting process, subjecting the resultant cast mass to ahomogenizing treatment, extruding and/or forging and/or machining thehomogenized cast mass and anodizing the resultant formed cast, therebyallowing the presence, in the anodized coat, of eutectic Si particles ofparticle diameters in the range of 0.4 to 5.5 μm and forming the coat ina thickness of 30 μm or more and with hardness Hv of 400 or more.

This invention also consists in a method for the production of a sleevepart excellent in hardness of an anodized coat and formed of an aluminumalloy, comprising casting an aluminum alloy of the composition mentionedabove by a continuous casting process, subjecting the resultant castmass to a homogenizing treatment, extruding and/or forging and/ormachining the homogenized cast mass and anodizing the resultant formedcast, thereby allowing the presence, in the anodized coat, of eutecticSi particles of particle diameters in the range of 0.4 to 5.5 μm andforming the coat in a thickness of 30 μm or more and with hardness Hv of400 or more.

The anodized coat produced as described above cannot form a crack. Thethickness and hardness of the coat mentioned above do not represent meretarget qualities, but indicate the qualities which can be attained byheeding and controlling the limits on the particle diameter distributionof eutectic Si particles in the anodized coat and the content of Cutherein.

This invention, as described above, concerns an aluminum alloy whichallows the presence of eutectic Si particles having particle diametersin the range of 0.4 to 5.5 μm in an anodized coat formed by an anodizingtreatment and permits manufacture of sleeve parts furnished with ananodized coat excelling in hardness and possessing resistance to wearand other wear-resistant aluminum alloy products which can be properlyutilized for automobile parts and other parts requiring the hardness andthickness of an anodized coat, shunning generation of a crack anddemanding wear resistance.

This aluminum alloy acquires sufficient hardness without requiring anyspecial anodizing treatment and, therefore, can be applied to parts thatare put to use without being anodized in advance.

This invention concerns an aluminum alloy which allows the presence ofeutectic Si particles having particle diameters in the range of 0.8 to5.5 μm in an anodized coat formed by an anodizing treatment and permitsmanufacture of sleeve parts furnished with an anodized coat excellingfurther in hardness and possessing wear resistance and otherwear-resistant aluminum alloy products.

The aluminum alloy of this invention is characterized by containing 5 to12% (mass %; similarly applicable hereinafter) of Si, 0.1 to 1% of Fe,less than 1% of Cu and 0.3 to 1.5% of Mg and having the balance formedof Al and impurities, having dispersed in the matrix thereof eutectic Siparticles of particle diameters in the range of 0.4 to 5.5 μm, inclusiveof 60% or more of the eutectic Si particles existing with particlediameters of 0.8 to 2.4 μm, and allowing the presence therein of 4000 ormore and less than 40000 eutectic Si particles per mm², therebypermitting manufacture of sleeve parts furnished with an anodized coatexcelling further in hardness and possessing a wear resistance and otherwear-resistant aluminum alloy products.

Further, the aluminum alloy of this invention, when containing 9 to 12%of Si, has 80% or more of the eutectic Si particles with particlediameters of 0.8 to 2.4 μm and therefore permits manufacture of sleeveparts furnished with an anodized coat excelling further in hardness andpossessing wear resistance and other wear-resistant aluminum alloyproducts.

The aluminum alloy of this invention contains substantially no Cu andtherefore acquires a further exalted ability to undergo an anodizingtreatment and permits provision of sleeve parts furnished with ananodized coat excelling further in hardness and possessing wearresistance and other wear-resistant aluminum alloy products.

The aluminum alloy of this invention contains one or two or morecomponents selected from among 0.1 to 1% of Mn, 0.04 to 0.3% of Cr, 0.04to 0.3% of Zr and 0.01 to 0.1% of V and, owing to the inclusion of Mn,Cr, Zr and V, induces precipitation of the Al—Mn type, Al—Mn—Fe—Si type,Al—Cr type, Al—Cr—Fe—Si type, Al—Zr type or Al—V type particles andthereby effects refinement of recrystallized particles, acquires exaltedworkability and permits formation of sleeve parts of complicated shapesand other wear-resistant aluminum alloy products. Further, the inclusionof Mn, Cr, Zr and V results in inducing precipitation of the particlesof the Al—Mn type, Al—Mn—Fe—Si type, Al—Cr type, Al—Cr—Fe—Si type, Al—Zrtype and Al—V type, suppressing recrystallization of the sleeve parts bya heat treatment given after the formation thereof and exalting theductility and toughness of the sleeve parts.

The aluminum alloy of this invention contains at least one componentselected from among 0.01 to 0.3% of Ti, 0.0001 to 0.05% of B and 0.001to 0.1% of Sr and, when containing Ti and B, induces refinement of thetexture of the cast mass, prevents the alloy mass from sustaining acrack during the course of forging, allows the aluminum alloy of thisinvention to be cast stably, further imparts exalted workability to thecast mass and permits manufacture of sleeve parts of complicated shapes.The inclusion of Sr results in allowing the eutectic Si particles to berefined and consequently enabling the aluminum alloy of this inventionto acquire improvement in ductility and toughness.

The aluminum alloy of this invention is a bar material cast by acontinuous casting process. This aluminum alloy, therefore, permitsmanufacture of sleeve parts excelling in hardness and possessing wearresistance and other wear-resistant aluminum alloy products.

The aluminum alloy of this invention is a bar material resulting fromsubjecting a bar material cast by a continuous casting process to anextruding process or an extruding and drawing process. Even when thesubsequent process omits a forging step or comprises a forging step of asmall processing ratio, it enjoys a sufficient processing ratio andacquires exalted ductility and toughness. It also permits easymanufacture of a bar material having a diameter of 20 mm or less whichis not easily obtained by the continuous casting technique.

The formed article which uses the bar material of the aluminum alloy ofthis invention mentioned above constitutes a product excellent inhardness and possessing wear resistance.

The bar material of the aluminum alloy of this invention mentioned abovepermits manufacture of a sleeve part possessing an anodized coat ofexcellent hardness and excelling in wear resistance.

The bar material of the aluminum alloy of this invention mentioned aboveundergoes a forging treatment. The forged part consequently obtainedpermits manufacture of sleeve parts furnished with an anodized coatexcelling in hardness and possessing wear resistance and otherwear-resistant aluminum alloy products.

The bar material or forged part of the aluminum alloy of this inventionmentioned above undergoes a machining treatment. The machined partconsequently obtained permits manufacture of sleeve parts furnished withan anodized coat excelling in hardness and possessing wear resistanceand other wear-resistant aluminum alloy products.

The aluminum alloy of this invention allows the presence, in an anodizedcoat, of eutectic Si particles of particle diameters in the range of 0.4to 5.5 μm and forms the coat in a thickness of 30 μm or more and withhardness Hv of 400 or more. The aluminum alloy product consequentlyobtained, therefore, excels in hardness of the anodized coat andpossesses wear resistance.

The aluminum alloy of this invention allows the presence, in an anodizedcoat, of eutectic Si particles of particle diameters in the range of 0.8to 5.5 μm and forms the coat in a thickness of 40 μm or more and withhardness Hv of 400 or more. The aluminum alloy product consequentlyobtained, therefore, excels in hardness of the anodized coat andpossesses wear resistance.

The machined part of the aluminum alloy of this invention has undergonea treatment for the formation of an anodized coat. It, therefore,constitutes a sleeve part that is furnished with an anodized coatexcelling in hardness and possessing wear resistance.

Then, the method for the production of an aluminum alloy according tothis invention comprises casting an aluminum alloy of the compositionmentioned above in accordance with a continuous casting process,subjecting the resultant cast mass to a homogenizing treatment,extruding and/or forging and/or machining the homogenized cast mass andanodizing the resultant formed cast, thereby allowing the presence, inan anodized coat, of eutectic Si particles of particle diameters in therange of 0.4 to 5.5 μm and forming the coat in a thickness of 30 μm ormore and with hardness Hv of 400 or more. The method, therefore, permitseasy manufacture of wear-resistant aluminum alloy products excelling inhardness of an anodized coat.

Then, the method for the production of an aluminum alloy according tothis invention comprises casting an aluminum alloy of the compositionmentioned above in accordance with a continuous casting process,subjecting the resultant cast mass to a homogenizing treatment,extruding and/or forging and/or machining the homogenized cast mass andanodizing the resultant formed cast, thereby allowing the presence, inan anodized coat, of eutectic Si particles of particle diameters in therange of 0.4 to 5.5 μm and forming the coat in a thickness of 30 μm ormore and with hardness Hv of 400 or more. The method, therefore, permitseasy manufacture of sleeve parts excelling in hardness of an anodizedcoat.

BEST MODE FOR CARRYING OUT THE INVENTION

The aluminum alloy according to this invention is characterized byinducing in consequence of an anodizing treatment the formation of ananodized coat having a thickness of 30 μm or more, preferably 40 μm ormore, and hardness Hv of 400 or more and the presence of eutectic Siparticles of particle diameters in the range of 0.4 to 5.5 μm,preferably 0.8 to 5.5 μm, in the coat.

The aluminum alloy mentioned above, in one preferred example of thecomposition thereof, contains 5 to 12% (mass %; similarly applicablehereinafter, preferably 5 to 11%) of Si, 0.1 to 1% of Fe, less than 1%(preferably less than 0.5% and more preferably substantially no content)of Cu and 0.3 to 1.5% (preferably 0.4 to 1%) of Mg, and has the balanceformed of Al and impurities.

The aluminum alloy mentioned above preferably contains at least onecomponent selected from among 0.1 to 1% of Mn, 0.04 to 0.3% of Cr; 0.04to 0.3% of Zr and 0.01 to 0.1% of V.

Preferably it further contains one or two or more components selectedfrom among 0.01 to 0.3% of Ti, 0.0001 to 0.05% of B and 0.001 to 0.1% ofSr.

The aluminum alloy of this composition excels in workability and abilityto yield to an anodizing treatment and acquires an ability to retain thehardness (Hv: 400 or more) of the anodized coat mentioned above.

It proves advantageous in respect that this aluminum alloy acquiressufficient hardness without undergoing any special anodizing treatmentand therefore fits application to parts that are put to use withoutrequiring an anodizing treatment.

Particularly, Si while coexisting with Mg induces precipitation of Mg₂Siparticles and exalts the strength of the aluminum alloy and, owing tothe distribution of eutectic Si, adds to strength and wear-resistance.The Si content is in the range of 5 to 12%, preferably 5 to 11%. If theSi content falls short of 5%, the shortage will prevent this effect ofSi from being manifested fully satisfactorily. If it exceeds 12%, theexcess will result in inducing precipitation of a primary crystal of Siand exerting an adverse effect to bear on the ability to undergo ananodizing treatment.

The Fe content is preferred to fall in the range of 0.1 to 1%(preferably 0.1 to 0.5% and more preferably 0.21 to 0.3%). The reasonfor this range is that the Fe content is capable of inducingprecipitation of the particles of the A—Fe type or A—Fe—Si type and,during the heat treatment after the formation of a sleeve part,repressing recrystallization and exalting the ductility and thetoughness of the sleeve part. Then, in the extruded material, the Fecontent is capable of refining recrystallized particles during thecourse of extrusion, exalting the forgeability of the material in thesubsequent step and consequently permitting manufacture of sleeve partsof complicated shapes. If the Fe content falls short of 0.1%, theshortage will prevent the effect of Fe from being manifestedsatisfactorily. If it exceeds 1%, the excess will result in increasingthe precipitation of coarse crystals of the A—Fe type or A—Fe—Si type,exerting an adverse effect to bear on the ability of the aluminum allyto succumb to an anodizing treatment and impairing the ductility and thetoughness of the aluminum alloy.

The Cu content is less than 1% (preferably 0.9% or less and morepreferably less than 0.5%) or substantially absent.

The inclusion of Cu results in inducing precipitation of CuAl₂ particlesand consequently contributing to the strength and hardness of thealuminum alloy. If the Cu content is 1% or more, the excess will resultin decreasing the hardness of the anodized coat. For the purpose offurther increasing the hardness of the coat, the Cu content is preferredto be less than 0.5% and more preferably to be substantially nil.

Cu is dissolved during the course of an anodizing treatment. Since theCu ions formed by this dissolution are precious metal ions, Cu isprecipitated again on the surface of the aluminum alloy matrix and issuffered to render the formation of an anodized coat difficult anddegrade the denseness of the coat. By controlling the Cu content, it ismade possible to exalt the formability and the denseness of the anodizedcoat and increase the hardness of the coat.

The coexistence of Mg and Si is effective in inducing precipitation ofMg₂Si particles and contributing to the strength of the aluminum alloy.The Mg content falls preferably in the range of 0.3 to 1.5% and morepreferably in the range of 0.4 to 1%. If the Mg content falls short of0.3%, the shortage will result in decreasing the effect. If it exceeds1.5%, the excess will results in lowering the workability of thealuminum alloy.

The inclusion of at least one component selected from among 0.1 to 1%(preferably 0.2 to 0.4%) of Mn, 0.04 to 0.3% (preferably 0.15 to 0.25%)of Cr, 0.04 to 0.3% (preferably 0.1 to 0.2%) of Zr and 0.01 to 0.1%(preferably 0.05 to 0.1%) of V in the composition of the aluminum alloymentioned above is effective in inducing precipitation of the particlesof the Al—Mn type, Al—Mn—Fe—Si type, Al—Cr type, Al—Cr—Fe—Si type, Al—Zrtype or Al—V type, suppressing recrystallization during the heattreatment after the formation of a sleeve part and exalting theductility and toughness of the sleeve part. Then, in the case of theextruded material, the inclusion is effective in refining therecrystallized particles during the course of the extrusion, exaltingthe forgeability of the extruded material in the subsequent step andconsequently enabling the sleeve part to be formed in a complicatedshape. If the Mn content falls short of 0.1%, the Cr content falls shortof 0.04%, the Zr content falls short of 0.04% and the V content fallsshort of 0.01%, these shortages will result in preventing the effects ofthese elements from being manifested satisfactorily. If the Mn contentexceeds 1%, the Cr content exceeds 0.3%, the Zr content exceeds 0.3% andthe V content exceeds 0.1%, their excesses will result in adding to theprecipitation of coarse crystals, exerting an adverse effect to bear onthe ability of the aluminum alloy to succumb to an anodizing treatmentand impairing the ductility and toughness of the aluminum alloy.

The inclusion of at least one component selected from among 0.01 to 0.3%(preferably 0.01 to 0.2% and more preferably 0.002 to 0.1%) of Ti,0.0001 to 0.05% (preferably 0.005 to 0.1%) of B and 0.001 to 0.2%(preferably 0.005 to 0.1% and more preferably 0.005 to 0.05%) of Sr isfavorable for the following reason. To be specific, the inclusion of Tiand B is effective in refining the texture of a cast mass, preventingthe cast mass from being fractured during the course of casting andexalting the workability of the cast mass and consequently permittingsleeve parts to be formed in complicated shapes. If the Ti content fallsshort of 0.01%, the shortage will result in preventing the effects ofits inclusion from being manifested sufficiently. If its content exceeds0.3%, the excess will result in inducing crystallization of giantintermetallic compound particles and exerting an adverse effect to bearon the aluminum alloy's workability and ability to succumb to ananodizing treatment. Then, the inclusion of Sr is effective in refiningthe eutectic Si and exalting the aluminum alloy's workability andability to succumb to an anodizing treatment. If the Sr content fallsshort of 0.001%, the shortage will prevent the effect of the inclusionfrom being manifested satisfactorily. If it exceeds 0.2%, the excesswill result in degrading the effect.

The Ni content is preferred to be 0.1% or less.

In this invention, it has been found that the state of distribution ofeutectic Si particles in an anodized coat is extremely important andfurther that the control thereof enables the coat to acquire a thicknessof 30 μm or more and hardness Hv of 400 or more and prevents the coatfrom generating a crack.

For this purpose, it is important to uniformly specify the state ofdispersion of eutectic Si in an alloy matrix. The aluminum alloy can beprecluded from sustaining a crack by allowing the presence of eutecticSi particles in the anodized coat and enabling the aluminum alloy toexcel in hardness of the coat and acquire an increased thickness.

To be specific, the eutectic Si particles dispersed in the alloy matrixhave particle diameters of 0.4 to 5.5 μm (preferably 0.8 to 5.5 μm). Itis proper and necessary that 60% or more (preferably 80% or more) of theeutectic Si particles have particle diameters of 0.8 to 2.4 μm and thatthe matrix allow the presence therein of 4000 or more and less than40000 (preferably 10000 or more and less than 38000) eutectic Siparticles per mm².

Incidentally, the expression “the eutectic Si particles have particlediameters of 0.4 to 5.5 μm” means that the substantial particle diameterdistribution is in the range of 0.4 to 5.5 μm. For example, it meansthat 95% or more, preferably 98% or more, of the eutectic Si particleshave particle diameters falling in the range of 0.4 to 5.5 μM.

The eutectic Si particles in the anodized coat have particle diametersof 0.4 to 5.5 μm as described above. If the particle diameters fallshort of 0.4 μm, particularly 0.3 μm, the shortage will result inheightening the voltage of the bath used for the anodizing treatment,increasing the resistance to the anodization, rendering the flow ofelectric current difficult and permitting no easy formation of the coat.If the particle diameters exceed 5.6 μm, particularly 6.0 μm, the excesswill result in forming a cause for degrading the ability of the aluminumalloy to succumb to an anodizing treatment and aggravating the surfacecoarseness of the formed coat.

Of the eutectic Si particles, those that have particle diameters of 0.8to 2.4 μm account for a proportion of 60% or more as described above. Ifthis proportion falls short of 60%, particularly within 50% inclusive,the shortage will result in increasing the difference between theportion allowing easy flow of electric current and the portion notallowing easy flow of electric current during the course of theanodizing treatment, disrupting the uniformity of flow of the electriccurrent and consequently preventing the formed coat from acquiring auniform thickness.

Particularly in the case of the Si content of 9 to 12% (especially10.5±0.5%) that finds a wide application for uses on the commercialscale, the proportion mentioned above is preferred to be 80% or more.

When the alloy matrix contains 4000 or more and less than 40000 eutecticSi particles of particle diameters of 0.8 to 2.4 μm per mm², the flow ofthe electric current during the course of the anodizing treatment isfixed and the produced coat is allowed to have a uniform thickness.Though the eutectic Si particles dispersed in the aluminum alloy matrixallow more difficult flow of electric current than the matrix, since thedifficulty can be suppressed, the anodized coat can be formed in auniform thickness. The degradation of the hardness of the coat can besuppressed further because the possibility of the eutectic Si survivingdissolution during the course of the anodizing treatment and persistingin the coat can be diminished and the possibility of the residualeutectic Si particles in the coat degrading the denseness of the coatsurrounding the eutectic Si particles can be suppressed.

To be more specific, the aluminum alloy of the composition mentionedabove is cast by the continuous casting process, such as the gaspressure hot top continuous casting process, the resultant cast mass issubjected to the homogenizing treatment, and the homogenized alloy massis either directly machined or subjected to a proper processing selectedfrom among extruding, forging and machining operations. By furthersubjecting the resultant formed aluminum alloy to the anodizingtreatment, it is made possible to obtain an aluminum alloy product whichexcels in hardness of the anodized coat and allows the coat to acquirean increased thickness without sustaining a crack.

The state of the generation of the eutectic Si in the alloy is affectedby the temperature of the melt of the alloy and the speed of castingwhile the melt of the alloy of the given composition is solidified bythe continuous casting process.

The aluminum alloy contemplated by this invention, therefore, can beobtained by controlling the temperature of the melt and the speed ofcasting, thereby enabling the eutectic Si particles to acquire particlediameters in the range of 0.4 to 5.5 μm. Further, by controlling thetemperature of the melt and the speed of casting, thereby enabling 60%or more of the eutectic Si particles to possess particle diameters of0.8 to 2.4 μm, it is made possible to obtain the aluminum alloy aimed atby this invention.

It is provided, however, that the speed of solidification must becontrolled to a rather higher level than ever because the aluminum alloyof this invention has a small Cu content, forms a small region ofsolid-liquid coexistence during solidification, and becomes liable tosolidify. In the case of a forging diameter of 72 mm, for example, thespeed of solidification is preferred to be in the range of 200 to 350mm/min.

The gas pressure hot top continuous casting process presses the gapbetween the melt and the mold with a gas and therefore permits the speedof casting to be increased. It is, therefore, at an advantage inpermitting easy production of the aluminum alloy of this inventionhaving the particle diameters of the eutectic Si controlled in a givenstate.

The state of generation of the eutectic Si in the alloy succumbs to theinfluences of the temperature of homogenization and the time ofhomogenization during the course of the homogenizing treatment andcontrols the particle diameter of the eutectic Si and controls the shapeof the eutectic Si particles as well.

By controlling the temperature of homogenization and the time ofhomogenization, thereby enabling the eutectic Si particles to assumeparticle diameters in the range of 0.4 to 5.5 μm, therefore, it is madepossible to obtain the aluminum alloy of this invention. Further, bycontrolling the temperature of homogenization and the time ofhomogenization, thereby enabling 60% or more of the eutectic Siparticles to assume particle diameters of 0.8 to 2.4 μm, it is madepossible to obtain the aluminum alloy of this invention.

Owing to the assumption of a granular form by the eutectic Si particles,the cast mass is enabled to have the workability thereof exalted ascompared with the acerate form prior to the anodizing treatment.Further, the ability of the aluminum alloy to succumb to an anodizingtreatment is exalted.

The homogenizing treatment does not need to be particularly restrictedbut is only required to satisfy the conditions mentioned above. It maybe properly carried out at a temperature of 450° C. or more and lowerthan 500° C. (preferably 480° C. or more) for a period of four hours ormore.

The primary crystal Si is preferred to be in the following state(position of distribution of particles, average particle diameter, andratio of occupation of area) or to be substantially absent from theouter peripheral part of the cast mass which is destined to form asleeve part in consequence of an anodizing treatment. If the primarycrystal Si is present in the part subjected to the anodizing treatment,it will prevent the flow of electric current from being fixed during thecourse of the anodizing treatment, render the thickness of the coatuneven, decrease the denseness of the coat and lower the hardness of thecoat.

Position of distribution of particles of primary crystal Si: Absent ofthe primary crystal Si from the outer periphery of the cast mass throughthe position of 20% or less of the radius of the cast mass (0.2% or lessof the ratio of occupation of area).

Average particle diameter of primary crystal Si: 30 μm or less.

Ratio of occupation of area by primary crystal Si: 0.8% or less.

For example, the procedure of setting the Si content at 12% or less andcontrolling the conditions of the amount of gas pressure, the speed ofcasting and the temperature of the melt during the course of a gaspressure hot top continuous casting operation is at an advantage inenabling the primary crystal Si to assume the state mentioned above.

The aluminum alloy mentioned above may be cast through the continuouscasting process to form cast billets and the cast billets may besubjected to a homogenizing treatment and then machined directly withoutbeing modified. Otherwise, the cast billets may be subjected to properlyselected processes, such as extruding, forging and machining operations.Alternatively, the aluminum alloy may be cast to manufacture barmaterials and the bar materials may be manufactured into formed articleshaving given shapes.

The manufacture of bar materials into formed articles may beaccomplished by properly combining various processes, such as machiningand forging operations. The bar materials are preferred to undergo anextruding or drawing process prior to the forging or machining process.The bar materials which have undergone the extruding or drawing processare at an advantage in enjoying exalted ductility and excelling inworkability and imparting ductility to end products. While round barsmeasuring 20 mm or less in diameter are not easily obtained by thecontinuous casting method, they can be easily obtained through theextruding or drawing process.

The extruding process does not need to be particularly restricted butmay be properly attained by using an extruding device of 2500 tons, forexample, and extruding a given bar material at the highest extrudingrate of 8 m/min.

The anodizing treatment that is performed on a formed article does notneed to be particularly restricted but may be properly accomplished byusing an aqueous 15-wt % sulfuric acid solution as the electrolyticbath.

The coat may be obtained in a given thickness by adjusting thetemperature of the bath, the electric voltage and the time of thetreatment.

The aluminum alloy of this invention and the sleeve parts manufacturedtherefrom can be effectively used in sleeve portions of more exactingrequirements because their matrix parts excel in hardness and theircoats enjoy an exalted ability to resist wear. They are suitable for thefollowing uses, for example.

-   (a) Compressor parts, such as scrolls and pistons, for use in air    conditioning devices.-   (b) Compressor pistons for use in automobile air suspensions.-   (c) Automobile engines, transmissions and ABS grade hydraulic parts,    such as spools and sleeves.-   (d) Brake master cylinder pistons/caliper pistons for automobiles-   (e) Clutch cylinder pistons for automobiles-   (f) Brake caliper bodies for automobiles

The wear-resistant aluminum alloy that is consequently obtained does notrestrict the uses to be found therefor. Among other automobile parts, itis particularly suitable for brake caliper pistons, air suspensionquality compressor pistons and other parts that require a coat excellingin hardness and defying infliction of a crack.

Examples of this invention will be explained below in contrast withComparative Examples.

Test 1

EXAMPLE 1

The aluminum alloys having the compositions shown in Table 1 weremanufactured by the gas pressure hot top continuous casting method intocast billets (8 inches in diameter). These cast billets were subjectedto a homogenizing treatment at 490° C. for 12 hours and extruded by anindirect extruding device to form extruded bars 44 mm in diameter. Theextruded bars were subjected to a T6 treatment performed by an ordinarymethod. The extruded bars resulting from this treatment were used astest materials and were tested for ability to succumb an anodizingtreatment, hardness of coat, presence or absence of the occurrence of acrack in the coat, wear resistance and mechanical properties based onthe standards shown below. The results of the test were rated. The testmaterials were further tested for determining the cross section,eutectic Si particles in an anodized coat and state of distribution ofparticle diameters by the use of an image analysis system under thefollowing conditions.

The determination was performed by cutting a given sample in anarbitrary size, embedding the cut sample in an abrading resin,micro-abrading the resin till eutectic Si particles became detectableand visually examining the abraded surface.

Conditions of determination: LUZEX joined to an optical microscope,magnifications on a picture plane: 1240, and calculated from the resultsof a continuous determination of 20 fields of view.

-   -   Thickness of coat: 44 to 47 μm

In the data shown in Table 1, those that deviated from the conditionsconforming to this invention are indicated with an underline.

Rating of Test 1

“Ability to Succumb to an Anodizing Treatment”

A cross section of a given extruded bar perpendicular to the directionof extrusion was cut till it formed a smooth surface having a fixedsurface roughness. The cross section was used as a sample for rating theability.

For the anodizing treatment, an aqueous 15-wt % sulfuric acid solutionwas used as the electrolytic bath and the anodizing treatment wasperformed, with the bath temperature, voltage and time so set as to forman anodized coat of a target thickness of 40 μm on the sample surface.

The cross section of the sample consequently obtained was visuallyobserved and measured for coat thickness with arbitrary 10 mm lengths.The ability of the sample to succumb to the anodizing treatment wasrated by the average thickness of the actually formed coat. Thethickness of the coat formed under the same conditions served as theindex for the ability to succumb to the anodizing treatment. The resultsare shown in Table 3.

-   ∘: Average coat thickness of 40 μm or more-   x: Average coat thickness of 33 μm or less-   Δ: Intermediate between ∘ and x.    “Coat Hardness”

The determination was performed by cutting a given sample which hadundergone an anodizing treatment in an arbitrary size, embedding the cutsample in a resin, micro-abrading the resin till the coat thicknessbecame detectable, and determining and rating the hardness of the coat.The results are shown in Table 3.

-   ∘: Average coat hardness Hv of 400 or more-   x: Average coat hardness Hv of 330 or less-   Δ: Intermediate between ∘ and x.    “Wear Resistance”

A given sample was tested for wear resistance by the use of an Ogoshiabrasion tester under the conditions of 1 m/s in speed of abrasion, 200m in distance of abrasion, 3.2 kg in load and S50C (Hv 750) in oppositematerial. The results were compared in terms of the relative amount ofwear. The results are shown in Table 2.

-   ∘: Less than 6.0×10⁻⁷ mm²/kg-   x: More than 9.0×10⁻⁷ mm²/kg-   Δ: 6.0 to 9.0×10⁻⁷ mm²/kg    “Crack in Coat”

A given sample that had undergone an anodizing treatment had the surfacecondition thereof observed under an optical microscope to determine andrate the presence or absence of a crack in the coat. The results areshown in Table 3.

-   ∘: Absence of a crack in the coat.-   x: Presence of a crack in the coat.    “Mechanical Properties”

A JIS No. 4 test piece was taken from the central part of an extrudedmaterial in parallel to the direction of extrusion and tested fortensile strength. The passage of the commendable tensile strength: 310(N/mm²) and proof strength: 230 (N/mm²) was taken as the standard. Theresults are shown in Table 2.

EXAMPLES 2 TO 13 AND COMPARATIVE EXAMPLES 1 TO 10

The same procedure as in Example 1 was repeated, with the compositionschanged as shown in Table 1. The conditions of forming an anodized coatwere the same as in Example 1.

It is clear from Table 2 and Table 3 that Examples 1 to 13 of thisinvention invariably excelled in ability to succumb to an anodizingtreatment, hardness of coat, freedom from infliction of a crack in thecoat and wear resistance, and were possessed of tensile strengthsexceeding 310 N/mm² and proof strengths exceeding 230 N/mm² as respectmechanical properties.

Comparative Example 1 was deficient in the ability to succumb to ananodizing treatment because it had a small Si content. Further,Comparative Examples 1, 2, 4, 5 and 8 were deficient in the ability tosuccumb to an anodizing treatment and in hardness of the coat becausethey had large Cu contents. TABLE 1 Composition (mass %) Test materialSi Fe Cu Mn Mg Cr Ti Sr Al Ex. 1 5.0 0.2 0.3 0.2 0.4 0.1 0.01 0.01Balance Ex. 2 5.0 0.2 0.4 0.2 0.4 0.1 0.01 0.01 Balance Ex. 3 5.0 0.20.9 0.2 0.4 0.1 0.01 0.01 Balance Ex. 4 5.0 0.2 0.9 0.2 0.8 0.1 0.010.01 Balance Ex. 5 7.5 0.2 0.4 0.2 0.4 0.1 0.01 0.01 Balance Ex. 6 7.50.2 0.9 0.2 0.4 0.1 0.01 0.01 Balance Ex. 7 7.5 0.2  0.95 0.2 0.8 0.10.01 0.01 Balance Ex. 8 8.1 0.2 0.6 0.2 0.4 0.1 0.01 0.01 Balance Ex. 910.1  0.2 0.3 0.2 0.4 0.1 0.01 0.01 Balance Ex. 10 10.1  0.2 0.4 0.2 0.40.1 0.01 0.01 Balance Ex. 11 10.1  0.2 0.4 0.2 0.8 0.1 0.01 0.01 BalanceEx. 12 10.5  0.2 0.9 0.2 0.4 0.1 0.01 0.01 Balance Ex. 13 10.5  0.2 0.90.2 0.8 0.1 0.01 0.01 Balance Comp. Ex. 1 4.5 0.2 2.5 0.2 1.1 0.1 — —Balance Comp. Ex. 2 7.0 0.2 3.0 0.2 1.1 0.1 — — Balance Comp. Ex. 3 7.50.2 1.4 0.2 0.3 0.1 — — Balance Comp. Ex. 4 7.5 0.2 2.5 0.2 0.4 0.1 — —Balance Comp. Ex. 5 8.2 0.2 2.5 0.2 0.6 0.1 — — Balance Comp. Ex 6 10.2 0.2 1.6 0.2 0.1 0.1 — 0.01 Balance Comp. Ex. 7 10.7  0.2 1.5 0.2 0.4 0.1— 0.01 Balance Comp. Ex. 8 10.5  0.2 2.7 0.2 0.4 0.1 — 0.01 BalanceComp. Ex. 9* 0.7 0.2 0.3 — 1.0 0.1 — — Balance Comp. Ex. 10* 0.8 0.2 0.40.2 1.0 0.2 — — Balance

TABLE 2 Tensile strength Proof strength Test material Wear resistanceσ′B (N/mm²) σ0.2 (N/mm²) Ex. 1 ∘ 312.0 234.0 Ex. 2 ∘ 337.3 252.3 Ex. 3 ∘343.3 240.6 Ex. 4 ∘ 389.4 272.1 Ex. 5 ∘ 343.5 241.5 Ex. 6 ∘ 350.0 258.7Ex. 7 ∘ 359.3 271.3 Ex. 8 ∘ 357.1 272.7 Ex. 9 ∘ 342.6 249.2 Ex. 10 ∘345.2 251.1 Ex. 11 ∘ 346.2 255.3 Ex. 12 ∘ 368.2 263.3 Ex. 13 ∘ 369.2273.4 Comp. Ex. 1 x 410.0 340.0 Comp. Ex. 2 ∘ 435.0 330.0 Comp. Ex. 3 ∘389.3 271.3 Comp. Ex. 4 ∘ 387.1 272.7 Comp. Ex. 5 ∘ 415.0 307.0 Comp.Ex. 6 ∘ 398.3 302.8 Comp. Ex. 7 ∘ 406.8 304.0 Comp. Ex. 8 ∘ 405.0 307.0Comp. Ex. 9 x 312.0 284.0 Comp. Ex. 10 x 289.9 252.3

TABLE 3 Pro- portion of Ability Thick- Diameter of eutectic NumberDistribution of diameters of eutectic Si particles (%) 0.8 to Hardnessto yield ness Test Si particles (μm) (pieces/ ≧0.8 ≧1.6 ≧2.4 ≧3.2 ≧4.0≧4.8 ≧5.5 5.6≦ 2.4 μm of coat anodization of coat material Max. Min.Ave. mm²) (μm) (μm) (μm) (μm) (μm) (μm) (μm) (μm) (%) (Hv) treatment(μm) Crack Ex. 1 4.32 0.80 2.20  9643 — 16.7 46.6 28.2 7.5 1.0 — — 63.3∘ 422 ∘ 47.1 ∘ Ex. 2 3.52 0.96 2.17  9740 — 14.9 46.6 31.6 6.9 — — —61.5 ∘ 412 ∘ 46.5 ∘ Ex. 3 4.96 0.80 2.18  9690 — 16.3 44.2 27.9 7.0 2.32.3 — 60.5 ∘ 405 ∘ 46.2 ∘ Ex. 4 4.32 0.96 2.05  9830 — 16.3 44.9 27.98.6 2.3 — — 61.2 ∘ 403 ∘ 41.3 ∘ Ex. 5 4.80 0.96 2.12 18737 — 21.4 45.824.2 6.7 1.6 0.3 — 67.2 ∘ 415 ∘ 47.3 ∘ Ex. 6 4.16 0.80 2.08 19245 — 22.044.0 27.1 6.6 0.3 — — 66.0 ∘ 403 ∘ 46.7 ∘ Ex. 7 4.16 0.80 2.06 22312 —19.6 46.1 23.5 9.8 1.0 — — 65.7 ∘ 409 ∘ 43.3 ∘ Ex. 8 3.84 0.80 1.9824415 — 21.6 46.8 22.7 8.9 — — — 68.4 ∘ 401 ∘ 41.1 ∘ Ex. 9 4.16 0.801.93 31450 — 31.7 46.8 18.9 2.5 0.1 — — 78.5 ∘ 410 ∘ 45.1 ∘ Ex. 10 3.520.80 1.81 35543 — 33.1 46.2 18.8 1.9 — — — 79.3 ∘ 413 ∘ 44.9 ∘ Ex. 113.36 0.80 1.85 33471 — 34.7 46.4 17.7 1.2 — — — 81.1 ∘ 409 ∘ 44.1 ∘ Ex.12 3.52 0.80 1.83 34768 — 34.5 47.6 16.1 1.8 — — — 82.1 ∘ 402 ∘ 44.4 ∘Ex. 13 3.35 0.80 1.87 32275 — 34.7 47.7 15.7 1.9 — — — 82.4 ∘ 402 ∘ 44.2∘ Comp. 4.78 0.96 2.30  8698 — 16.7 45.3 27.3 6.5 2.6 1.6 — 62.0 x 325 Δ38.5 ∘ Ex. 1 Comp. 4.75 0.92 2.17 18698 — 19.4 44.6 25.6 7.5 2.9 — —64.0 x 298 x 32.2 ∘ Ex. 2 Comp. 4.58 0.90 2.18 21987 — 21.4 44.2 25.38.3 0.8 — — 65.6 Δ 381 Δ 39.5 ∘ Ex. 3 Comp. 4.51 0.96 2.05 22098 — 21.645.6 24.5 7.6 0.7 — — 67.2 x 324 Δ 39.1 ∘ Ex. 4 Comp. 4.33 0.80 2.0825349 — 21.8 46.4 23.6 7.4 0.8 — — 68.2 x 322 Δ 37.8 ∘ Ex. 5 Comp. 3.630.80 1.93 32115 — 33.2 46.6 18.7 1.5 — — — 79.8 Δ 365 Δ 38.3 ∘ Ex. 6Comp. 3.56 0.80 1.81 35543 — 32.8 46.8 18.8 1.6 — — — 79.6 Δ 374 Δ 38.6∘ Ex. 7 Comp. 3.45 0.80 1.85 33471 32.6 46.4 18.6 2.0 0.4 — — 79.0 x 313Δ 37.8 ∘ Ex. 8 Comp. — — — — — — — — — — — — — ∘ 475 ∘ 44.1 x Ex. 9Comp. — — — — — — — — — — — — — ∘ 477 ∘ 44.3 x Ex. 10

Comparative Examples 9 and 10 showed no discernible sign of eutectic Siparticle.

The diameter and the distribution of eutectic Si particles are theresults of measuring in a cross section. TABLE 4 Distribution ofdiameters of eutectic Si particles in anodized coat Distribution ofDiameter of diameters of Proportion eutectic Number eutectic Siparticles (%) of 0.8 to Test Si particles (μm) (pieces/ ≧0.8 ≧1.6 ≧2.4≧3.2 ≧4.0 ≧4.8 ≧5.5 5.6≦ 2.4 μm material Max. Min. Ave. mm²) (μm) (μm)(μm) (μm) (μm) (μm) (μm) (μm) (%) Ex. 3 4.86 0.80 2.11  9530 — 16.7 44.427.9 6.9 2.0 2.1 — 61.1 Ex. 6 4.06 0.80 2.02 19143 — 22.4 43.6 28.1 5.80.1 — — 66.0 Ex. 12 3.32 0.80 1.80 34595 — 35.2 48.1 15.7 1.0 — — — 83.3Test 2 (Bar Material Formed by Hot Top Continuous Casting, Bar MaterialFormed by Hot Top Continuous Casting+Forging)

An aluminum alloy having the composition shown in Table 5 wasmanufactured by the gas pressure hot top continuous casting methoddisclosed in JP-B SHO 54-42827 into bar materials of a diameter of 72mm. The bar materials were then subjected to a homogenizing treatment at490° C. for four hours and subjected to a T6 treatment according to anordinary method under the conditions shown in Table 6 (a solutiontreatment at 500 to 510° C. for two to three hours, followed by watercooling and further by an aging treatment at 180 to 190° C. for five tosix hours) to obtain test materials. Otherwise, the continuous casting(continuously cast) bar materials were similarly subjected to ahomogenizing treatment, then to a shaving treatment to remove the castskin, cut to given lengths, and the cut lengths were subjected to anannealing treatment and a bonde treatment, and forged into double wallcups measuring 68 mm in outside diameter of the outer cup, 52 mm ininside diameter of the outer cup, 32 mm in outside diameter of the innercup, 15 mm in inside diameter of the inner cup, 40 mm in height and 10mm in bottom thickness. These double wall cups were subjected to a T6treatment according to the ordinary method under the conditions shown inTable 8 (a solution treatment at 500 to 510° C. for two to three hours,following by water cooling and further by an aging treatment at 180 to190° C. for five to six hours) to obtain forged parts as test materials.The test materials were further machined and thereafter tested forability to succumb to an anodizing treatment, hardness of coat, thepresence or absence of a crack in the coat, wear resistance andmechanical properties under the following standards. They were alsotested for the cross section of test material, eutectic Si particles inthe anodized coat and distribution of particle diameters by the use ofan image analysis system under the conditions shown below.

The determination was performed through cutting a given sample in anarbitrary size, embedding the cut sample in a resin and micro-abradingthe resin till eutectic Si particles became detectable.

-   -   Conditions of determination: Magnifications on a picture plane:        1240, and calculated from the results of a continuous        determination of 20 fields of view.    -   Thickness of coat: 25 to 47 μm

In the data shown in Table 5, those that deviated from the conditionsconforming to this invention are indicated with an underline.

Test 3 (Bar Material Obtained by Horizontal Continuous Casting, BarMaterial Obtained by Horizontal Continuous Casting+Forging)

An aluminum alloy having the composition shown in Table 5 wasmanufactured by the horizontal continuous casting method disclosed inJP-A SHO 61-33735 into bar materials of a diameter of 30 mm. The barmaterials were then subjected to a homogenizing treatment at 490° C. forfour hours and to a T6 treatment according to an ordinary method underthe conditions shown in Table 20 (a solution treatment at 500 to 510° C.for two to three hours, followed by water cooling and further by anaging treatment at 180 to 190° C. for five to six hours) to obtain testmaterials. Otherwise, the continuously cast bar materials were similarlysubjected to a homogenizing treatment and then to a shaving treatment toremove the cast skin, and cut to given lengths, and the cut lengths weresubjected to an annealing treatment and a bonde treatment, and forgedinto cups measuring 32 mm in outside diameter, 15 mm in inside diameter,27 mm in height and 8 mm in bottom thickness. These cups were subjectedto a T6 treatment according to the ordinary method under the conditionsshown in Table 8 (a solution treatment at 500 to 510° C. for two tothree hours, following by water cooling and further by an agingtreatment at 180 to 190° C. for five to six hours) to obtain forgedparts as test materials. The test materials were further machined andthereafter tested for ability to succumb to an anodizing treatment,hardness of coat, presence or absence of a crack in the coat, wearresistance and mechanical properties under the following standards. Theywere also tested for the cross section of test material, eutectic Siparticles in the anodized coat and distribution of particle diameters bythe use of an image analysis system under the conditions shown below.

The determination was performed by cutting a given sample in anarbitrary size, embedding the cut sample in a resin, micro-abrading theresin till eutectic Si particles became detectable.

-   -   Conditions of determination: magnifications on a picture plane        of the image analysis system: 1240, and calculated from the        results of a continuous determination of 20 fields of view.    -   Thickness of coat: 25 to 47 μm

In the data shown in Table 5, those (Comparative Examples) that deviatedfrom the conditions conforming to this invention are indicated with anunderline.

Test 4 (Extruded Material/Drawn Material, Extruded Material/DrawnMaterial+Forging)

An aluminum alloy having the composition shown in Table 5 wasmanufactured using the gas-pressure hot top continuous casting methoddisclosed in JP-B SHO 54-42827 into billets (8 inches in diameter).Then, the cast billets were subjected to a homogenizing treatment at490° C. for four hours. Subsequently, the cast mass was heated to 350°C. and then extruded by the use of an indirect extruding device tomanufacture extruded bars 32 mm in diameter and subjected to a T6treatment according to an ordinary method under the conditions shown inTable 20 (a solution treatment at 500 to 510° C. for two to three hours,followed by water cooling, and further by an aging treatment at 180 to190° C. for five to six hours) to obtain extruded bars as testmaterials. Otherwise, the indirectly extruded bars were drawn into bars39.2 mm in diameter, subjected to a T6 treatment by an ordinary methodunder the conditions shown in Table 6 (a solution treatment at 500 to510° C. for two to three hours, followed by water cooling and further byan aging treatment at 180 to 190° C. for five to six hours) to obtaindrawn bars as test materials. Alternatively, the drawn bars 39.2 mm indiameter manufactured from the extruded bars were cut into givenlengths, subjected to an annealing treatment and a bonde treatment, andforged into cups measuring 32 mm in outside diameter, 15 mm in insidediameter, 27 mm in height and 8 mm in bottom thickness. These cups weresubjected to a T6 treatment by the ordinary method under the conditionsshown in Table 8 (a solution treatment at 500 to 510° C. for two tothree hours, followed by water cooling and further by an aging treatmentat 180 to 190° C. for five to six hours) to obtain forged parts as testmaterials, machined and subsequently tested for ability to succumb to ananodizing treatment, hardness of a coat, presence or absence of a crackin the coat, wear resistance and mechanical properties by the standardshown below. They were also tested for the cross section of testmaterial, eutectic Si particles in the anodized coat and distribution ofparticle diameters by the use of an image analysis system under theconditions shown below.

The determination was performed by cutting a given sample in anarbitrary size, embedding the cut sample in a resin, micro-abrading theresin till eutectic Si particles became detectable.

-   -   Conditions of determination: Magnifications on a picture plane        of the image analysis system: 1240, and calculated from the        results of a continuous determination of 20 fields of view.    -   Thickness of coat: 25 to 47 μm

In the data shown in Table 5, those that deviated from the conditionsconforming to this invention are indicated with an underline.

Evaluation of Tests 2 to 4

“Ability to Succumb to Anodizing Treatment”

A cross section of a given extruded bar perpendicular to the directionof extrusion was cut till it formed a smooth surface having a fixedsurface roughness. The cross section was used as a sample for rating theability.

For the anodizing treatment, an aqueous 15-wt % sulfuric acid solutionwas used as the electrolytic bath and the anodizing treatment wasperformed with the bath temperature, electric voltage and time so set asto form an anodized coat of a target thickness of 30 μm on the samplesurface.

The cross section of the sample consequently obtained was visuallyobserved and measured for coat thickness with arbitrary 10 mm lengths.The ability of the sample to succumb to the anodizing treatment wasrated by the average thickness of the actually formed coat. Thethickness of the coat formed under the same conditions served as theindex for the ability to succumb to the anodizing treatment. The largerthe thickness, the better the ability is. The results obtained ofsamples having undergone no forging treatment are shown in Table 7 andthose obtained of samples having undergone a forging treatment are shownin Table 9.

-   ∘: Average coat thickness of 30 μm or more-   x: Average coat thickness of less than 30 μm

While the preceding test 1 used a target thickness of 40 μm, the presenttests 2 to 4 used a target thickness of 30 μm on account of the largetotal number of samples. Therefore, the standard for the rating was asshown above.

“Hardness of Coat”

The determination was performed through cutting a given sample in anarbitrary size, embedding the cut sample in a resin and micro-abradingthe resin till eutectic Si particles became detectable. The hardness ofthe coat was measured and rated. The results of the samples that had notundergone a forging treatment are shown in Table 6 and those of thesamples that had undergone the forging treatment are shown in Table 8.

“Wear Resistance”

A given sample was tested for relative wear resistance by the use of anOgoshi abrasion tester under the conditions of 1 m/s in speed ofabrasion, 200 m in distance of abrasion, 3.2 kg in load and S50C (Hv:750) in opposite material. The results obtained of the sample that hadnot undergone any forging treatment are shown in Table 6 and those ofthe samples that had undergone the forging treatment are shown in Table8.

-   ∘: Less than 6.0×10⁻⁷ mm²/kg-   x: More than 9.0×10⁻⁷ mm²/kg-   Δ: 6.0 to 9.0×10⁻⁷ mm²/kg    “Crack in Coat”

A given sample that had undergone an anodizing treatment was visuallyobserved through a magnifying mirror having 10 or more magnifications toconfirm and rate the presence or absence of a crack. The results of thesamples that had not undergone a forging treatment are shown in Table 7and those of the samples that had undergone the forging treatment areshown in Table 9.

The results are shown in Table 3.

-   ∘: No crack in the coat-   x: A crack found in the coat    “Mechanical Properties”

A JIS No. 4 test piece was taken from the central part of an extrudedmaterial in parallel to the direction of extrusion and tested fortensile strength. The passage of the commendable tensile strength of 310N/mm² and proof strength of 230 N/mm² was taken as the standard. Theresults are shown in Table 6.

“Product Test, Brake Caliper Piston”

The continuously cast materials, extruded materials and drawn materialsof Examples 101 to 104, 121 to 125, 141 to 144 and 150 to 153 having thecompositions shown in Table 1 and the forced products thereof (Example201 to 204, 221 to 225, 241 to 244 and 250 to 253) were manufactured bymachining into brake caliper pistons. These brake caliper pistons weresubjected to a T6 treatment by following the ordinary method to formanodized coats of 38 μm or more on their surfaces. These brake caliperpistons were incorporated into brake master cylinders of four wheelersand were made to repeat braking operations to determine the conditionsof seizure and locking. For the purpose of comparison, the aluminumalloys of Comparative Examples 101, 104, 108, 109, 111, 114, 115, 118 to120 and 124 to 126 having the compositions shown in Table 1 weresimilarly manufactured to form brake caliper pistons and tested.

With 500,000 braking motions as the common standard, the brake caliperpistons of Example 101 to 153 and Examples 201 to 253 and those of theComparative Examples produced no sign of problem. When the test wasfurther continued with the braking motions increased up to 1,000,000times, the brake caliber pistons of Examples 11 to 153 and Examples 201to 253 sustained absolutely no scar, whereas those of the ComparativeExamples sustained streaky scratches. The brake caliper pistons usingthe aluminum alloys of Comparative Examples 125 and 126 and having thecompositions shown in Table 1 could not be put to the test because theysustained cracks on their surfaces. TABLE 5 Material Composition (wt %)Method of production Si Fe Cu Mn Mg Cr Ti Sr Ex. 101 Hot top continuousforging 5.0 0.25 — — 0.4 — — — Ex. 102 Horizontal continuous ″ ″ ″ ″ ″ ″″ ″ forging Ex. 103 Extruding ″ ″ ″ ″ ″ ″ ″ ″ Ex. 104 Extruding/drawing″ ″ ″ ″ ″ ″ ″ ″ Ex. 105 Hot top continuous forging 5.0 0.25 — — 0.8 — —— Ex. 106 Hot top continuous forging 5.0 0.25 0.4 — 0.4 — — — Ex. 107Hot top continuous forging 5.0 0.25 0.9 — 0.4 — — — Ex. 108 Horizontalcontinuous ″ ″ ″ ″ ″ ″ ″ ″ forging Ex. 109 Extruding ″ ″ ″ ″ ″ ″ ″ ″ Ex.110 Extruding/drawing ″ ″ ″ ″ ″ ″ ″ ″ Ex. 111 Hot top continuous forging5.0 0.25 0.9 — 0.8 — — — Ex. 112 Hot top continuous forging 5.0 0.25 0.90.2 0.4 — — — Ex. 113 Hot top continuous forging 5.0 0.25 0.9 0.2 0.80.1 — — Ex. 114 Hot top continuous forging 5.0 0.25 0.9 0.2 0.5 0.1 —0.015 Ex. 115 Hot top continuous forging 5.0 0.25 0.9 0.2 0.5 0.1 0.015— Ex. 116 Hot top continuous forging 7.0 0.25 — — 0.4 — — — Ex. 117Horizontal continuous ″ ″ ″ ″ ″ ″ ″ ″ forging Ex. 118 Extruding ″ ″ ″ ″″ ″ ″ ″ Ex. 119 Extruding/drawing ″ ″ ″ ″ ″ ″ ″ ″ Ex. 120 Hot topcontinuous forging 7.0 0.25 — — 0.8 — — — Ex. 121 Hot top continuousforging 7.0 0.25 0.4 — 0.4 — — — Ex. 122 Hot top continuous forging 7.00.25 0.9 — 0.8 — — — Ex. 123 Horizontal continuous ″ ″ ″ ″ ″ ″ ″ ″forging Ex. 124 Extruding ″ ″ ″ ″ ″ ″ ″ ″ Ex. 125 Extruding/drawing ″ ″″ ″ ″ ″ ″ ″ Ex. 126 Hot top continuous forging 7.0 0.25 0.9 0.2 0.4 — —— Ex. 127 Hot top continuous forging 7.0 0.25 0.9 0.2 0.8 0.1 — — Ex.128 Hot top continuous forging 7.0 0.25 0.4 0.2 0.5 0.1 — 0.015 Ex. 129Hot top continuous forging 7.0 0.25 0.4 0.2 0.5 0.1 0.015 Ex. 130 Hottop continuous forging 8.2 0.25 0.6 — 0.4 — — — Ex. 131 Hot topcontinuous forging 10.0  0.25 — — 0.4 — — — Ex. 132 Horizontalcontinuous ″ ″ ″ ″ ″ ″ ″ ″ forging Ex. 133 Extruding ″ ″ ″ ″ ″ ″ ″ ″ Ex.134 Extruding/drawing ″ ″ ″ ″ ″ ″ ″ ″ Ex. 135 Hot top continuous forging10.0  0.25 — — 0.8 — — — Ex. 136 Hot top continuous forging 10.0  0.25 —— 0.4 — — 0.015 Ex. 137 Hot top continuous forging 10.0  0.25 0.4 — 0.4— — — Ex. 138 Horizontal continuous ″ ″ ″ ″ ″ ″ ″ ″ forging Ex. 139Extruding ″ ″ ″ ″ ″ ″ ″ ″ Ex. 140 Extruding/drawing ″ ″ ″ ″ ″ ″ ″ ″ Ex.141 Hot top continuous forging 10.0  0.25 0.9 — 0.4 — — — Ex. 142Horizontal continuous ″ ″ ″ ″ ″ ″ ″ ″ forging Ex. 143 Extruding ″ ″ ″ ″″ ″ ″ ″ Ex. 144 Extruding/drawing ″ ″ ″ ″ ″ ″ ″ ″ Ex. 145 Hot topcontinuous forging 10.0  0.25 0.9 — 0.8 — — — Ex. 146 Hot top continuousforging 10.0  0.25 0.9 0.2 0.4 — — — Ex. 147 Hot top continuous forging10.0  0.25 0.9 0.2 0.8 0.1 — — Ex. 148 Hot top continuous forging 10.5 0.25  0.95 — 0.8 — — — Ex. 149 Hot top continuous forging 10.5  0.25 0.40.2 0.4 0.1 — 0.015 Ex. 150 Hot top continuous forging 10.5  0.25 0.9 —0.4 — — 0.015 Ex. 151 Extruding ″ ″ ″ ″ ″ ″ ″ ″ Ex. 152Extruding/drawing ″ ″ ″ ″ ″ ″ ″ ″ Ex. 153 Hot top continuous forging10.5  0.25 0.9 0.2 0.8 0.1 0.015 — Comp. Ex. Hot top continuous forging4.5 0.25 2.5 — 1.1 — — — 101 Comp. Ex. Horizontal continuous ″ ″ ″ ″ ″ ″″ ″ 102 forging Comp. Ex. Extruding ″ ″ ″ ″ ″ ″ ″ ″ 103 Comp. Ex.Extruding/drawing ″ ″ ″ ″ ″ ″ ″ ″ 104 Comp. Ex. Hot top continuousforging 7.0 0.25 3.0 — 1.1 — — — 105 Comp. Ex. Hot top continuousforging 7.0 0.25 3.0 0.2 1.1 0.1 — — 106 Comp. Ex. Hot top continuousforging 7.5 0.25 1.4 — 0.3 — — — 107 Comp. Ex. Hot top continuousforging 7.5 0.25 2.5 0.2 0.4 — — — 108 Comp. Ex. Horizontal continuous ″″ ″ ″ ″ ″ ″ ″ 109 forging Comp. Ex. Extruding ″ ″ ″ ″ ″ ″ ″ ″ 110 Comp.Ex. Extruding/drawing ″ ″ ″ ″ ″ ″ ″ ″ 111 Comp. Ex. Hot top continuousforging 8.5 0.25 2.5 0.2 0.6 0.1 — — 112 Comp. Ex. Hot top continuousforging 10.3  0.25 1.6 — 0.1 — — — 113 Comp. Ex. Hot top continuousforging 10.6  0.25 1.5 — 0.4 — — — 114 Comp. Ex. Horizontal continuous ″″ ″ ″ ″ ″ ″ ″ 115 forging Comp. Ex. Extruding ″ ″ ″ ″ ″ ″ ″ ″ 117 Comp.Ex. Extruding/drawing ″ ″ ″ ″ ″ ″ ″ ″ 118 Comp. Ex. Hot top continuousforging 10.5  0.25 1.6 — 0.5 — 0.015 — 119 Comp. Ex. Hot top continuousforging 10.7  0.25 1.5 — 0.5 — — 0.015 120 Comp. Ex. Hot top continuousforging 10.5  0.25 2.7 0.2 0.4 — — 0.015 121 Comp. Ex. Extruding ″ ″ ″ ″″ ″ ″ ″ 122 Comp. Ex. Extruding/drawing ″ ″ ″ ″ ″ ″ ″ ″ 123 Comp. Ex.Hot top continuous forging 10.6  0.25 2.5 0.2 0.4 0.1 — 0.015 124 Comp.Ex. Extruding/drawing 0.7 0.25 0.3 — 1.0 0.2 0.015 — 125 Comp. Ex.Extruding/drawing 1.0 0.25 — 0.8 0.8 — 0.015 — 126

TABLE 6 Heat-treating conditions/mechanical properties of cast bars andextruded material Mechanical property 0.2% Tensile proof strengthstremgth Elongation Hardness Wear T6 condition (N/mm²) (N/mm²) (%) (HRB)resistance Ex. 101 510° C. × 2.5 hrs → Water cooling → 180° C. × 6 hrs322 244 17.9 59.7 ∘ Ex. 102 ″ 325 246 18.3 59.8 ∘ Ex. 103 ″ 318 239 18.559.2 ∘ Ex. 104 ″ 316 238 18.9 58.9 ∘ Ex. 105 ″ 333 263 17.5 61.6 ∘ Ex.106 ″ 338 275 17.4 63.1 ∘ Ex. 107 500° C. × 2.5 hrs → Water cooling →190° C. × 6 hrs 358 302 16.5 67.6 ∘ Ex. 108 ″ 360 305 16.9 67.8 ∘ Ex.109 ″ 356 299 17.0 67.2 ∘ Ex. 110 ″ 354 297 17.4 67.0 ∘ Ex. 111 ″ 366310 15.5 68.7 ∘ Ex. 112 ″ 355 298 16.6 67.7 ∘ Ex. 113 ″ 363 307 16.168.8 ∘ Ex. 114 ″ 356 300 16.4 67.8 ∘ Ex. 115 ″ 352 297 16.7 67.7 ∘ Ex.116 510° C. × 2.5 hrs → Water cooling → 180° C. × 6 hrs 320 249 16.659.9 ∘ Ex. 117 ″ 322 250 17.0 60.1 ∘ Ex. 118 ″ 315 244 17.3 59.5 ∘ Ex.119 ″ 313 241 17.6 59.1 ∘ Ex. 120 ″ 330 266 15.8 61.9 ∘ Ex. 121 ″ 336276 15.6 63.4 ∘ Ex. 122 500° C. × 2.5 hrs → Water cooling → 190° C. × 6hrs 363 311 14.0 69.0 ∘ Ex. 123 ″ 365 315 14.2 69.2 ∘ Ex. 124 ″ 360 30914.5 68.6 ∘ Ex. 125 ″ 358 306 14.9 68.3 ∘ Ex. 126 ″ 353 299 15.0 68.1 ∘Ex. 127 ″ 361 309 14.4 69.1 ∘ Ex. 128 510° C. × 2.5 hrs → Water cooling→ 180° C. × 6 hrs 337 275 15.7 63.6 ∘ Ex. 129 ″ 335 274 15.6 63.9 ∘ Ex.130 500° C. × 2.5 hrs → Water cooling → 190° C. × 6 hrs 340 278 13.965.1 ∘ ∘ Ex. 131 510° C. × 2.5 hrs → Water cooling → 180° C. × 6 hrs 317242 13.4 60.4 ∘ ∘ Ex. 132 ″ 318 244 13.6 60.5 ∘ Ex. 133 ″ 314 237 13.960.1 ∘ Ex. 134 ″ 311 235 14.1 59.9 ∘ Ex. 135 ″ 327 268 13.0 62.3 ∘ Ex.136 ″ 318 240 13.6 60.3 ∘ Ex. 137 ″ 333 279 12.6 63.8 ∘ Ex. 138 ″ 334280 12.9 63.8 ∘ Ex. 139 ″ 329 274 13.1 63.4 ∘ Ex. 140 ″ 327 273 13.463.2 ∘ Ex. 141 500° C. × 2.5 hrs → Water cooling → 190° C. × 6 hrs 349297 11.6 68.4 ∘ Ex. 142 ″ 351 299 11.8 68.5 ∘ Ex. 143 ″ 347 294 12.068.1 ∘ Ex. 144 ″ 345 292 12.2 67.9 ∘ Ex. 145 ″ 360 312 10.5 69.3 ∘ Ex.146 ″ 350 300 11.0 68.6 ∘ Ex. 147 ″ 358 314 10.4 69.5 ∘ Ex. 148 ″ 360313 10.2 70.1 ∘ Ex. 149 510° C. × 2.5 hrs → Water cooling → 180° C. × 6hrs 336 281 12.8 64.3 ∘ Ex. 150 500° C. × 2.5 hrs → Water cooling → 190°C. × 6 hrs 350 301 11.6 68.7 ∘ Ex. 151 ″ 347 294 12.1 68.3 ∘ Ex. 152 ″346 293 12.3 68.1 ∘ Ex. 153 ″ 356 312 10.4 70.5 ∘ Comp. Ex. 495° C. ×2.5 hrs → Water cooling → 190° C. × 6 hrs 415 373 13.9 73.1 Δ 101 Comp.Ex. ″ 416 372 14.3 73.0 Δ 102 Comp. Ex. ″ 411 368 14.6 72.6 Δ 103 Comp.Ex. ″ 409 367 14.7 72.4 Δ 104 Comp. Ex. ″ 417 378 12.1 73.9 ∘ 105 Comp.Ex. ″ 410 365 12.0 74.1 ∘ 106 Comp. Ex. ″ 376 321 13.6 71.4 ∘ 107 Comp.Ex. ″ 410 363 13.1 74.3 ∘ 108 Comp. Ex. ″ 412 365 13.2 74.4 ∘ 109 Comp.Ex. ″ 407 359 13.6 74.0 ∘ 110 Comp. Ex. ″ 406 357 13.7 73.9 ∘ 111 Comp.Ex. ″ 411 366 12.7 74.5 ∘ 112 Comp. Ex. ″ 319 244 11.5 60.7 ∘ 113 Comp.Ex. ″ 383 328 10.2 72.0 ∘ 114 Comp. Ex. ″ 386 330 10.4 72.3 ∘ 115 Comp.Ex. ″ 380 324 10.9 71.7 ∘ 117 Comp. Ex. ″ 378 321 11.2 71.5 ∘ 118 Comp.Ex. ″ 387 331 9.7 72.2 ∘ 119 Comp. Ex. ″ 384 329 10.3 72.1 ∘ 120 Comp.Ex. ″ 405 358 9.3 74.9 ∘ 121 Comp. Ex. ″ 401 354 9.7 74.4 ∘ 122 Comp.Ex. ″ 399 351 10.0 74.2 ∘ 123 Comp. Ex. ″ 403 357 9.4 74.6 ∘ 124 Comp.Ex. 530° C. × 2.5 hrs → Water cooling → 180° C. × 6 hrs 334 290 22.964.1 x 125 Comp. Ex. ″ 333 294 20.8 64.7 x 126

TABLE 7 Particle diameters of cast bars and extruded material/anodizedcoat properties Eutectic Si Anodized coat Ave. Max. Min. ProportionAbility Thickness particle particle particle Number of yield to Hardnessof diameter diameter diameter pieces/ 0.8 to 2.4 μm anodization of coatcoat (μm) (μm) (μm) mm² (%) treatment (Hv) (μm) Crack Ex. 101 2.02 4.810.4 10,012 64.1 ∘ 432 ∘ 46.8 ∘ Ex. 102 1.91 4.43 0.4 10,889 66.3 ∘ 433 ∘46.9 ∘ Ex. 103 2.24 5.26 0.8  9,222 61.5 ∘ 431 ∘ 46.7 ∘ Ex. 104 2.255.21 0.8  9,334 60.8 ∘ 430 ∘ 46.6 ∘ Ex. 105 2.01 4.81 0.4 10,043 64.3 ∘431 ∘ 46.2 ∘ Ex. 106 2.00 4.79 0.4 10,057 64.5 ∘ 422 ∘ 43.2 ∘ Ex. 1071.99 4.78 0.4 10,065 64.4 ∘ 410 ∘ 41.1 ∘ Ex. 108 1.90 4.46 0.4 10,90766.5 ∘ 411 ∘ 41.0 ∘ Ex. 109 2.23 5.23 0.8  9,235 61.8 ∘ 409 ∘ 41.1 ∘ Ex.110 2.24 5.28 0.8  9,332 61.6 ∘ 408 ∘ 41.0 ∘ Ex. 111 2.00 4.79 0.4 9,992 64.3 ∘ 407 ∘ 40.8 ∘ Ex. 112 1.99 4.78 0.4  9,983 64.7 ∘ 408 ∘41.0 ∘ Ex. 113 1.98 4.77 0.4 10,004 64.2 ∘ 406 ∘ 40.7 ∘ Ex. 114 1.914.48 0.4 10,616 67.6 ∘ 409 ∘ 41.0 ∘ Ex. 115 2.01 4.80 0.4 10,032 64.1 ∘408 ∘ 40.7 ∘ Ex. 116 1.96 4.70 0.4 20,115 68.7 ∘ 430 ∘ 45.8 ∘ Ex. 1171.88 4.30 0.4 21,633 70.8 ∘ 429 ∘ 45.7 ∘ Ex. 118 2.20 5.12 0.8 18,57366.0 ∘ 427 ∘ 45.8 ∘ Ex. 119 2.19 5.15 0.8 18,495 65.7 ∘ 428 ∘ 45.7 ∘ Ex.120 1.97 4.72 0.4 20,104 69.0 ∘ 427 ∘ 45.4 ∘ Ex. 121 1.96 4.70 0.420,135 68.8 ∘ 416 ∘ 42.4 ∘ Ex. 122 1.98 4.67 0.4 20,121 69.1 ∘ 406 ∘40.6 ∘ Ex. 123 1.89 4.32 0.4 21,602 71.3 ∘ 405 ∘ 40.4 ∘ Ex. 124 2.215.14 0.8 18,532 66.7 ∘ 406 ∘ 40.5 ∘ Ex. 125 2.22 5.16 0.8 18,486 66.5 ∘405 ∘ 40.4 ∘ Ex. 126 1.97 4.70 0.4 20,114 68.9 ∘ 407 ∘ 40.3 ∘ Ex. 1271.98 4.72 0.4 20,103 69.3 ∘ 405 ∘ 40.1 ∘ Ex. 128 1.90 4.34 0.4 21,73171.7 ∘ 414 ∘ 40.5 ∘ Ex. 129 1.97 4.72 0.4 20,170 68.5 ∘ 411 ∘ 40.3 ∘ Ex.130 1.95 4.68 0.4 25,334 72.3 ∘ 407 ∘ 40.2 ∘ Ex. 131 1.93 4.64 0.434,007 80.6 ∘ 427 ∘ 44.9 ∘ Ex. 132 1.79 4.00 0.4 35,863 83.7 ∘ 428 ∘44.8 ∘ Ex. 133 2.16 5.20 0.8 32,142 78.5 ∘ 428 ∘ 44.7 ∘ Ex. 134 2.145.23 0.8 32,263 78.1 ∘ 427 ∘ 44.7 ∘ Ex. 135 1.95 4.60 0.8 33,989 80.9 ∘426 ∘ 44.4 ∘ Ex. 136 1.79 3.94 0.8 34,060 83.1 ∘ 428 ∘ 44.9 ∘ Ex. 1371.93 4.54 0.8 34,071 81.1 ∘ 416 ∘ 42.0 ∘ Ex. 138 1.78 3.98 0.4 35,89184.1 ∘ 417 ∘ 41.9 ∘ Ex. 139 2.07 5.06 0.4 32,154 79.2 ∘ 416 ∘ 41.9 ∘ Ex.140 2.09 5.08 0.8 32,276 79.0 ∘ 416 ∘ 41.8 ∘ Ex. 141 1.91 4.48 0.434,084 82.6 ∘ 405 ∘ 39.9 ∘ Ex. 142 1.83 4.14 0.4 35,908 84.7 ∘ 405 ∘39.8 ∘ Ex. 143 2.10 5.00 0.8 32,182 80.3 ∘ 404 ∘ 39.8 ∘ Ex. 144 2.095.02 0.8 32,297 80.1 ∘ 404 ∘ 39.8 ∘ Ex. 145 1.91 4.57 0.4 34,170 83.3 ∘403 ∘ 39.3 ∘ Ex. 146 1.89 4.52 0.4 34,139 82.9 ∘ 406 ∘ 39.6 ∘ Ex. 1471.91 4.56 0.4 34,269 83.4 ∘ 404 ∘ 39.2 ∘ Ex. 148 19.2 4.60 0.4 34,28683.5 ∘ 404 ∘ 39.0 ∘ Ex. 149 1.77 3.92 0.4 35,188 84.9 ∘ 417 ∘ 40.1 ∘ Ex.150 1.76 3.92 0.4 35,201 85.3 ∘ 407 ∘ 39.7 ∘ Ex. 151 1.98 4.37 0.834,163 82.2 ∘ 406 ∘ 39.8 ∘ Ex. 152 1.99 4.39 0.8 34,194 82.1 ∘ 406 ∘39.6 ∘ Ex. 153 1.91 4.56 0.4 33,948 83.4 ∘ 404 ∘ 39.0 ∘ Comp. Ex. 1012.02 4.88 0.4  9,224 63.2 x 324 x 31.7 ∘ Comp. Ex. 102 1.92 4.52 0.4 9,976 65.6 x 325 x 31.5 ∘ Comp. Ex. 103 2.26 5.30 0.8  8,766 61.2 x 324x 31.6 ∘ Comp. Ex. 104 2.28 5.34 0.8  8,704 61.1 x 324 x 31.6 ∘ Comp.Ex. 105 1.98 4.76 0.4 20,346 70.2 x 297 x 29.6 ∘ Comp. Ex. 106 1.97 4.740.4 20,359 70.3 x 296 x 29.4 ∘ Comp. Ex. 107 1.96 4.81 0.4 21,052 69.5 Δ384 Δ 35.8 ∘ Comp. Ex. 108 1.95 4.78 0.4 21,084 69.9 x 325 x 30.7 ∘Comp. Ex. 109 1.89 4.76 0.4 22,251 72.2 x 324 x 30.5 ∘ Comp. Ex. 1102.22 5.20 0.8 18,724 67.9 x 325 x 30.6 ∘ Comp. Ex. 111 2.21 5.18 0.818,745 67.8 x 326 x 30.5 ∘ Comp. Ex. 112 1.94 4.67 0.4 26,118 72.8 x 322x 29.9 ∘ Comp. Ex. 113 1.92 4.63 0.4 34,225 82.1 Δ 389 Δ 34.6 ∘ Comp.Ex. 114 1.91 4.58 0.4 34,286 82.4 Δ 381 Δ 34.1 ∘ Comp. Ex. 115 1.81 4.400.4 35,946 85.3 Δ 382 Δ 34.0 ∘ Comp. Ex. 117 2.14 5.06 0.8 32,945 79.8 Δ380 Δ 34.0 ∘ Comp. Ex. 118 2.16 5.08 0.8 33,017 79.6 Δ 380 Δ 33.9 ∘Comp. Ex. 119 1.92 4.54 0.4 34,346 82.3 Δ 379 Δ 33.7 ∘ Comp. Ex. 1201.81 4.10 0.4 35,347 85.4 Δ 381 Δ 34.1 ∘ Comp. Ex. 121 1.82 4.08 0.435,459 85.8 x 323 x 29.7 ∘ Comp. Ex. 122 2.07 5.02 0.8 34,428 81.9 x 322x 29.6 ∘ Comp. Ex. 123 2.08 5.00 0.8 34,481 81.8 x 320 x 29.5 ∘ Comp.Ex. 124 1.80 4.06 0.4 35,878 85.3 x 323 x 29.7 ∘ Comp. Ex. 125 — — — — —∘ 462 ∘ 47.1 x Comp. Ex. 126 — — — — — ∘ 469 ∘ 47.3 x

TABLE 8 Heat treatment conditions for forged parts Production method ofForging Hardness Wear material for forging treatment T6 conditions (HRB)resistance Ex. 201 Ex. 101 Hot top Presence 510° C. × 2.5 hr → 59.2 ∘continuous Water cooling → forging 180° C. × 6 hrs Ex. 207 Ex. 107 Hottop Presence 500° C. × 2.5 hr → Water cooling → 190° C. × 6 hrs 67.0 ∘continuous forging Ex. 208 Ex. 108 Horizontal Presence ″ 67.3 ∘continuous forging Ex. 210 Ex. 110 Extruding/ Presence ″ 66.4 ∘ drawingEx. 216 Ex. 116 Hot top Presence 510° C. × 2.5 hr → Water cooling → 180°C. × 6 hrs 59.3 ∘ continuous forging Ex. 217 Ex. 117 Horizontal Presence″ 59.4 ∘ continuous forging Ex. 219 Ex. 119 Extruding/ Presence ″ 58.4 ∘drawing Ex. 221 Ex. 121 Hot top Presence ″ 62.8 ∘ continuous forging Ex.222 Ex. 122 Hot top Presence 500° C. × 2.5 hr → Water cooling → 190° C.× 6 hrs 68.3 ∘ continuous forging Ex. 223 Ex. 123 Horizontal Presence ″68.6 ∘ continuous forging Ex. 225 Ex. 125 Extruding/ Presence ″ 67.5 ∘drawing Ex. 228 Ex. 128 Hot top Presence 510° C. × 2.5 hr → 62.8 ∘continuous Water cooling → forging 180° C. × 6 hrs Ex. 231 Ex. 131 Hottop Presence 510° C. × 2.5 hr → Water cooling → 180° C. × 6 hrs 59.7 ∘continuous forging Ex. 232 Ex. 132 Horizontal Presence ″ 59.7 ∘continuous forging Ex. 234 Ex. 134 Extruding/ Presence ″ 59.1 ∘ drawingEx. 237 Ex. 137 Hot top Presence ″ 63.2 ∘ continuous forging Ex. 238 Ex.138 Horizontal Presence ″ 63.1 ∘ continuous forging Ex. 240 Ex. 140Extruding/ Presence ″ 62.4 ∘ drawing Ex. 241 Ex. 141 Hot top Presence500° C. × 2.5 hr → Water cooling → 190° C. × 6 hrs 67.5 ∘ continuousforging Ex. 242 Ex. 142 Horizontal Presence ″ 67.7 ∘ continuous forgingEx. 243 Ex. 143 Extruding Presence ″ 67.4 ∘ Ex. 244 Ex. 144 Extruding/Presence ″ 67.3 ∘ drawing Ex. 245 Ex. 145 Hot top Presence ″ 68.5 ∘continuous forging Ex. 250 Ex. 150 Hot top Presence 500° C. × 2.5 hr →Water cooling → 190° C. × 6 hrs 67.9 ∘ continuous forging Ex. 252 Ex.152 Extruding/ Presence ″ 67.4 ∘ drawing Ex. 253 Ex. 153 Hot topPresence ″ 69.9 ∘ continuous forging Comp. Ex. Comp. Ex. Hot topPresence 495° C. × 2.5 hr → Water cooling → 190° C. × 6 hrs 72.6 Δ 201101 continuous forging Comp. Ex. Comp. Ex. Hot top Presence ″ 73.3 ∘ 205105 continuous forging Comp. Ex. Comp. Ex. Hot top Presence ″ 73.4 ∘ 206106 continuous forging Comp. Ex. Comp. Ex. Hot top Presence ″ 73.7 ∘ 208108 continuous forging Comp. Ex. Comp. Ex. Horizontal Presence ″ 73.8 ∘209 109 continuous forging Comp. Ex. Comp. Ex. Extruding/ Presence ″73.4 ∘ 211 111 drawing Comp. Ex. Comp. Ex. Hot top Presence ″ 71.4 ∘ 214114 continuous forging Comp. Ex. Comp. Ex. Horizontal Presence ″ 71.8 ∘215 115 continuous forging Comp. Ex. Comp. Ex. Extruding/ Presence ″70.9 ∘ 218 118 drawing Comp. Ex. Comp. Ex. Hot top Presence ″ 71.5 ∘ 219119 continuous forging Comp. Ex. Comp. Ex. Hot top Presence ″ 71.5 ∘ 220120 continuous forging Comp. Ex. Comp. Ex. Hot top Presence ″ 74.1 ∘ 221121 continuous forging Comp. Ex. Comp. Ex. Extruding Presence ″ 73.5 ∘222 122 Comp. Ex. Comp. Ex. Extruding/ Presence ″ 73.5 ∘ 223 123 drawingComp. Ex. Comp. Ex. Extruding/ Presence 530° C. × 2.5 hr → Water cooling→ 180° C. × 6 hrs 63.5 x 225 125 drawing Comp. Ex. Comp. Ex. Extruding/Presence ″ 64.2 x 226 126 drawing

TABLE 9 Particle diameters of cast bars and extruded material/anodizedcoat properties Eutectic Si Anodized coat Ave. Max. Min. ProportionAbility to Thickness particle particle particle Number of yield toHardness of diameter diameter diameter pieces/ 0.8 to 2.4 μm anodizationof coat coat (μm) (μm) (μm) mm² (%) treatment (Hv) (μm) Crack Ex. 2012.03 4.82 0.4 10,003 63.9 ∘ 433 ∘ 46.7 ∘ Ex. 207 2.01 4.79 0.4 10,05564.3 ∘ 411 ∘ 40.9 ∘ Ex. 208 1.91 4.48 0.4 10,896 66.3 ∘ 413 ∘ 41.1 ∘ Ex.210 2.25 5.31 0.8  9,323 61.3 ∘ 410 ∘ 40.8 ∘ Ex. 216 1.98 4.71 0.420,106 68.5 ∘ 431 ∘ 45.6 ∘ Ex. 217 1.89 4.32 0.4 21,623 70.5 ∘ 431 ∘45.6 ∘ Ex. 219 2.21 5.18 0.8 18,485 65.5 ∘ 430 ∘ 45.8 ∘ Ex. 221 1.974.72 0.4 20,123 68.5 ∘ 417 ∘ 42.5 ∘ Ex. 222 2.00 4.68 0.4 20,108 68.7 ∘408 ∘ 40.8 ∘ Ex. 223 1.90 4.34 0.4 21,593 71.0 ∘ 406 ∘ 40.5 ∘ Ex. 2252.24 5.17 0.8 18,472 66.1 ∘ 407 ∘ 40.2 ∘ Ex. 228 1.91 4.36 0.4 21,71671.5 ∘ 415 ∘ 40.4 ∘ Ex. 231 1.95 4.65 0.4 33,994 80.2 ∘ 429 ∘ 45.1 ∘ Ex.232 1.80 4.01 0.4 35,852 83.4 ∘ 429 ∘ 44.9 ∘ Ex. 234 2.15 5.24 0.832,248 77.9 ∘ 429 ∘ 44.9 ∘ Ex. 237 1.95 4.56 0.8 34,055 80.8 ∘ 417 ∘42.1 ∘ Ex. 238 1.79 3.99 0.4 35,878 83.8 ∘ 419 ∘ 42.0 ∘ Ex. 240 2.115.11 0.8 32,264 78.8 ∘ 417 ∘ 42.0 ∘ Ex. 241 1.92 4.50 0.4 34,072 82.2 ∘406 ∘ 39.8 ∘ Ex. 242 1.85 4.15 0.4 35,895 84.5 ∘ 407 ∘ 39.9 ∘ Ex. 2432.13 5.01 0.8 32,169 80.0 ∘ 405 ∘ 39.9 ∘ Ex. 244 2.10 5.04 0.8 32,28079.7 ∘ 404 ∘ 40.0 ∘ Ex. 245 1.92 4.59 0.4 34,152 83.0 ∘ 404 ∘ 39.2 ∘ Ex.250 1.78 3.96 0.4 35,180 85.1 ∘ 407 ∘ 39.6 ∘ Ex. 252 2.01 4.42 0.834,171 81.8 ∘ 407 ∘ 39.4 ∘ Ex. 253 1.93 4.59 0.4 33,924 83.0 ∘ 406 ∘38.9 ∘ Comp. Ex. 201 2.04 4.90 0.4  9,199 63.0 x 326 x 31.9 ∘ Comp. Ex.205 2.00 4.78 0.4 20,321 69.7 x 298 x 29.7 ∘ Comp. Ex. 206 1.99 4.76 0.420,331 70.1 x 296 x 29.5 ∘ Comp. Ex. 208 1.97 4.79 0.4 21,072 69.6 x 327x 30.9 ∘ Comp. Ex. 209 1.91 4.78 0.4 22,238 71.8 x 324 x 30.6 ∘ Comp.Ex. 211 2.22 5.21 0.8 18,731 67.6 x 328 x 30.6 ∘ Comp. Ex. 214 1.94 4.600.4 34,261 82.1 Δ 382 Δ 34.2 ∘ Comp. Ex. 215 1.84 4.42 0.4 35,923 84.9 Δ384 Δ 33.9 ∘ Comp. Ex. 218 2.18 5.11 0.8 32,991 79.3 Δ 381 Δ 33.8 ∘Comp. Ex. 219 1.93 4.55 0.4 34,317 82.0 Δ 381 Δ 33.5 ∘ Comp. Ex. 2201.82 4.12 0.4 35,318 85.0 Δ 382 Δ 33.9 ∘ Comp. Ex. 221 1.84 4.11 0.435,433 85.5 x 324 x 29.6 ∘ Comp. Ex. 222 2.08 5.03 0.8 34,402 81.7 x 324x 29.5 ∘ Comp. Ex. 223 2.11 5.03 0.8 34,457 81.5 x 322 x 29.3 ∘ Comp.Ex. 225 — — — — — ∘ 463 ∘ 47 x Comp. Ex. 226 — — — — — ∘ 471 ∘ 47.2 x

TABLE 10 Material Eutectic Si in anodized coat Ave. particle Max.particle Min. particle Proportion of diameter diameter diameter Number0.8 to 2.4 μm (μm) (μm) (μm) (pieses/mm²) (%) 1.98 4.79 0.4  9,689 63.82.20 5.17 0.8  8,961 60.6 1.96 4.65 0.4 19,711 68.4 2.04 5.04 0.8 31,68178.5 1.87 4.43 0.4 33,463 82 1.78 4.08 0.4 35,282 84 2.03 4.95 0.831,455 80.1 2.05 4.99 0.8 31,663 79.8

TABLE 11 Forged parts Eutectic Si in anodized coat Ave. particle Max.particle Min. particle Proportion of diameter diameter diameter Number0.8 to 2.4 μm (μm) (μm) (μm) (pieses/mm²) (%) 1.98 4.78 0.4  9,503 63.61.91 4.67 0.4 19,582 68.0 1.88 4.44 0.4 33,329 81.6 1.80 4.10 0.4 35,11083.8 2.06 4.97 0.8 31,400 79.3 2.05 4.99 0.8 31,495 79.1

Industrial Applicability

The aluminum alloy according to this invention derives from an anodizingtreatment that results in the presence of eutectic Si particles in theanodized coat, is endowed with excellent wear resistance and can be usedfor:

-   (a) Air-conditioner grade compressor parts, such as scrolls and    pistons-   (b) Compressor pistons for use in air suspensions of automobiles-   (c) Spools and sleeves for automobile engines, and transmission and    ABS hydraulic parts-   (d) Brake master cylinder pistons/caliper pistons for automobiles-   (e) Clutch cylinder pistons for automobiles-   (f) Brake caliper bodies for automobiles

It is particularly suitable for brake caliper pistons and air suspensiongrade compressor pistons and other parts that require a coat excellingin hardness and defying infliction of a crack.

1. An aluminum alloy that forms in consequence of an anodizing treatmentan anodized coat having a thickness of 30 μm or more and hardness Hv of4000 or more and allows a presence, in the coat, of eutectic Siparticles having particle diameters in the range of 0.4 to 5.5 μm.
 2. Analuminum alloy that forms in consequence of an anodizing treatment ananodized coat having a thickness of 40 μm or more and hardness Hv of4000 or more and allows a presence, in the coat, of eutectic Siparticles having particle diameters in a range of 0.8 to 5.5 μm.
 3. Analuminum alloy according to claim 1 or claim 2, which contains 5 to 12%(mass %; similarly applicable hereinafter) of Si, 0.1 to 1% of Fe, lessthan 1% of Cu and 0.3 to 1.5% of Mg, and has the balance formed of Aland impurities, has dispersed in a matrix thereof eutectic Si particleshaving particle diameters in a range of 0.4 to 5.5 μm, inclusive of 60%or more of the eutectic Si particles having particle diameters of 0.8 to2.4 μm, and allows a presence of 4000 or more and less than 40000eutectic Si particles per mm².
 4. An aluminum alloy according to any oneof claims 1 to 3, which when containing 9 to 12% of Si, has 80% or moreof the eutectic Si particles with particle diameters of 0.8 to 2.4 μm.5. An aluminum alloy according to any one of claims 1 to 4, whichcontains substantially no Cu.
 6. An aluminum alloy according to any oneof claims 1 to 5, further containing at least one component selectedfrom among 0.1 to 1% of Mn, 0.04 to 0.3% of Cr, 0.04 to 0.3% of Zr and0.01 to 0.1% of V.
 7. An aluminum alloy according to any one of claims 1to 6, further comprising at least one component selected from among 0.01to 0.3% of Ti, 0.0001 to 0.05% of B and 0.001 to 0.1% of Sr.
 8. Analuminum alloy according to any one of claims 1 to 7, wherein thealuminum alloy is a bar material cast by a continuous casting method. 9.An aluminum alloy according to any one of claims 1 to 7, wherein thealuminum alloy is a bar material manufactured by a continuous castingmethod and then extruded or extruded and drawn.
 10. A bar materialcomprising the aluminum alloy according to any one of claims 1 to
 9. 11.A bar material according to claim 10, wherein the bar material is usedas a sleeve part.
 12. A forged article resulting from subjecting the barmaterial according to claim 10 or claim 11 to a forging process.
 13. Amachined article resulting from subjecting the bar material according toclaim 10 or claim 11 or the forged article according to claim 12 to amachining process.
 14. A wear-resistant aluminum alloy having ananodized coat having a thickness of 30 μm or more and hardness Hv of400, which allows a presence, in the anodized coat, of eutectic Siparticles of particle diameters in a range of 0.4 to 5.5 μM.
 15. Awear-resistant aluminum alloy excelling in hardness of an anodized coat,which allows a presence, in an anodized coat, of eutectic Si particlesof particle diameters in a range of 0.8 to 5.5 μm and forms the coat ina thickness of 40 μm or more and with hardness Hv of 400 or more.
 16. Asleeve part excelling in hardness of an anodized coat, resulting fromsubjecting the machined article according to claim 13 to an anodizingtreatment.
 17. A method for the production of a wear-resistant aluminumalloy excelling in hardness of an anodized coat, comprising casting thealuminum alloy according to any one of claims 3 to 7 by a continuouscasting process to form a cast mass, homogenizing the cast mass to forma homogenized cast mass, then extruding and/or forging and/or machiningthe homogenized cast mass to form a formed cast mass and subjecting theformed cast mass to an anodizing treatment, thereby allowing a presence,in the anodized coat, of eutectic Si particles of particle diameters ina range of 0.4 to 5.5 μm and forming the coat in a thickness of 30 μm ormore and with hardness Hv of 400 or more.
 18. A method for theproduction of a sleeve part excelling in hardness of an anodized coatand formed of an aluminum alloy, comprising casting the aluminum alloyaccording to any one of claims 3 to 7 by a continuous casting process toform a cast mass, homogenizing the cast mass to form a homogenized castmass, then extruding and/or forging and/or machining the homogenizedcast mass to form a formed cast mass and subjecting the formed cast massto an anodizing treatment, thereby allowing a presence, in the anodizedcoat, of eutectic Si particles of particle diameters in a range of 0.8to 5.5 μm and forming the coat in a thickness of 40 μm or more and withhardness Hv of 400 or more.